Block copolymers of the ABA type, composed of a poly(ethylene/butylene) elastomeric mid block B and two polystyrene thermoplastic end blocks A, have been known for a long time and are abbreviated to SEBS.
Such products are marketed for example by SHELL under the trade name KRATON®.
These polymers are widely used in numerous applications such as the production of molded articles, for example shoe soles or coverings, or as binders or plasticizers in a variety of products and formulations, and finally as adhesives. Given their hydrocarbon nature, these SEBS copolymers are very hydrophobic and consequently are deficient in numerous applications, for example those requiring adhesion to a polar surface.
Therefore, there is also a modified SEBS whose elastomeric mid block contains a functional group chosen so as to allow the creation of interactions with polar surfaces.
This product is an SEBS maleic anhydride marketed by SHELL under the name KRATON G 1901®, which contains about 2% by weight of succinic anhydride groups attached to the poly(ethylene/butylene) mid chain.
The presence of succinic anhydride groups distributed along the mid chain thus affords a better adhesion to glass, textiles and metals.
However, although they have excellent mechanical properties and a good solubility in organic solvents, the hydrophobic nature of all these modified or unmodified SEBS makes them incompatible with hydrophilic products, which are consequently very difficult, if not impossible, to incorporate into formulations or products based on SEBS.
Although this incompatibility is certainly of no concern in applications such as the production of molded articles or coverings, it presents many more problems especially when these SEBS are used as adhesives, particularly in contact with skin or mucosae. In this case they are a basic component of formulations or products into which it is often desirable to incorporate hydrophilic compounds, for example for the production of patches in pharmacy or cosmetology, for the production of dressings in the treatment of blisters or corns, or in dermatology.
Thus, in this case, the incorporation of hydrophilic compounds, for example simply water, or an antiseptic, for example chlorhexidine digluconate, can be very useful or even essential. Now, the hydrophobic nature of the existing SEBS makes this incorporation very complex, if not impossible, depending on the nature or amounts of the hydrophilic compounds to be introduced.
As the products obtained are unstable, they require the incorporation of additives, which complicate their production, increase the cost, may introduce irritation problems, etc.
Likewise, the capacity of SEBS to absorb water or hydrophobic liquids is virtually zero. Thus, when they are used in the treatment of wounds, they are regularly mixed with other absorbent materials, such as cellulose derivatives, alginates or the like, to give an absorbent final product. The problem, as before, is that this physical mixing complicates the production of the formulations (problems of compatibility, viscosity, particle size, etc.), increases the risks of loss of cohesion of the product due to absorption, etc.
It would therefore be useful to have SEBS copolymers, particularly for the production of formulations that may or may not adhere to skin, wounds or mucosae, which have a better affinity towards hydrophilic compounds and liquids, thereby making it possible to solve the problems of formulation and absorption described above. It would also make it possible to extend the application interval and fields of application of these polymers.
The present invention relates to novel amphiphilic SEBS copolymers which meet these objectives and make it possible to solve these problems of the compatibility between SEBS and hydrophilic compounds and the affinity of SEBS for hydrophilic liquids.
Thus, according to a first feature, the present patent application aims to cover amphiphilic block copolymers of the ABA type containing two polystyrene thermoplastic end blocks A and one elastomeric mid block B, wherein this mid block B is a poly(ethylene/butylene) block containing grafted hydrophilic groups, it being possible for said amphiphilic copolymer ABA to be represented schematically by the following structure:
in which R1 and R2, which are identical or different, are hydrophilic groups with an average molecular weight below 10,000, selected from the following groups:
in which n, a and b are integers.
Advantageously, within the framework of the present invention, preferred amphiphilic copolymers will be those in which R1 and R2 are identical.
Among these amphiphilic copolymers, it will be preferable to use those in which R1 and R2 are a group CH3—O—(CH2—CH2—O)n, particularly those for which the average molecular weight of the group CH3—O—(CH2—CH2—O)n varies between 1000 and 8000, and very particularly that which has an average molecular weight of 2000, i.e. n=45.